Expression of Transcription Factor GATA-6 in Alveolar Epithelial Cells Is Linked to Neonatal Lung Disease

Abstract

Background: Premature birth and respiratory distress syndrome (RDS) are risk factors for disturbed lung development and bronchopulmonary dysplasia (BPD). The molecular mechanisms related to prematurity and BPD remain largely unknown. Epithelial expression of the transcription factor GATA-6 has been implicated in normal and abnormal murine lung development.

Objectives: The possible involvement of GATA-6 in the normal development and in RDS and BPD was investigated in the human and baboon lung.

Methods: Immunohistochemistry was used to study the expression of GATA-6 and thyroid transcription factor 1 in lung specimens from different age groups of human and baboon fetuses and newborns with lung disease. Furthermore, the regulatory role of TGF-β₁ in GATA-6 expression was investigated in human pulmonary epithelial cell lines using RT-PCR.

Results: GATA-6 expression increased in the developing human airway epithelium along with advancing gestation, but diminished to negligible at birth. In RDS, GATA-6 expression was enhanced at 5-7 days after birth, and decreased thereafter. In BPD, the expression of GATA-6 in alveolar epithelial cells was low. These results were confirmed and extended using an established baboon model of prematurity. The in vitro experiments revealed that TGF-β₁ induces GATA-6 and thyroid transcription factor 1 expression in lung epithelial cells.

Conclusions: Our results suggest that the expression of GATA-6 at the early stages of the preterm lung may be related to impaired postnatal alveolar development.

Fig. 1

Expression of GATA-6 and TTF-1 transcription factors in human fetal (a and b) and term (c and d) lungs. Both GATA-6 and TTF-1 are expressed in the developing fetal airspaces, but not in term lungs. Bars = 200 μm (a–d). Arrowheads point at developing airspace epithelium (b) and alveolar epithelium (d).

Fig. 2

Immunohistochemical staining with specific antibodies for GATA-6 and TTF-1 transcription factors at various stages of human RDS (GATA-6: a, c, e; TTF-1: b, d, f) and in BPD (GATA-6: g; TTF-1: h). Note that the expression of GATA-6 and TTF-1 is highest in RDS prolonged for 3–7 days (c and d). Bars = 200 μm (a–h).

Fig. 3

Immunohistochemical staining with an antibody for GATA-6 transcription factor in baboon RDS and BPD. In RDS, enhanced GATA-6 immunoreactivity was observed in the terminal airspaces (arrow), bronchiolar epithelium (br) and arterial wall (ar) of 125 + 6 days PRN O₂ baboons (b) compared with age-matched GCs (a; 125 days' gestation). a Alveolar epithelium is marked by an arrow. In evolving BPD, GATA-6 expression decreased in the bronchiolar epithelium (br) of 125 + 14 days PRN O₂ animals (d) when compared with age-matched fetal controls (c; 140 days' gestation GCs). Arrows point at alveolar epithelium. ca = Capillaries. Bars = 400 μm (a–d).

Fig. 4

Expression of GATA-6 (a), GATA-4 (b), TTF-1 (c) and GAPDH (d) mRNA as detected by RT-PCR in A549 cell line presented as boxplots (median, 25th and 75th percentile and the highest and lowest value presented from at least three experiments quantitated densitometrically, and a representative gel is shown below each boxplot).